1. Field of the Invention
This invention relates in general to computer systems and, more particularly to a display control system for personal computer systems.
2. Description of the Related Art
Personal computer systems in general and IBM compatible personal computer systems in particular have attained widespread use. These personal computing systems now provide computing power to many segments of today's modern society. A personal computer system can usually be defined as a desktop, floor-standing, or portable microcomputer that includes a system unit having a system processor with associated volatile and non-volatile memory, a display monitor, a keyboard, one or more floppy diskette drives, a hard disk storage device and an optional printer. One of the distinguishing characteristics of these systems is the use of a system board or mother board to electrically connect these components together. These personal computer systems are information handling systems which are designed primarily to give independent computing power to a single user and are inexpensively priced for purchase by individuals or small businesses.
Portable computers are often referred to as laptop, notebook or subnotebook computers. These computers typically incorporate a flat panel display, which is a relatively small video display with a shallow physical depth based on technology other than the cathode-ray tube (CRT), such as a liquid crystal display (LCD). Portable computers often provide for coupling to a conventional standalone display monitor. Many portable computers incorporate some strategy for automatically and incrementally dimming the entire flat panel display to conserve power. These are typically implemented via "activity timers" which start dimming the display when periods of inactivity on devices such as the mouse and keyboard exceed a preset threshold. However, these strategies are limited by current flat panel technology which can only dim or brighten the entire display surface at once which renders the display monitor more difficult to view as more power is saved. Most flat panels utilize a single "backlight" to control panel brightness. Power consumption of laptop displays is directly related to the brightness of the "backlight" bulb, therefore, the entire display screen must be dimmed in order to reduce power consumption. Maintaining a high level of brightness on the display monitor is one of the most significant factors detrimentally effecting battery life. It is also one of the most problematic to address with typical flat panel display technology.
A new display technology, compatible for use with portable computers, is the electron beam flat panel display technology. An electron beam flat panel display monitor 80, illustrated in FIG. 1, utilizes large arrays of individually controllable cold-cathode field emission devices 85 (electron guns) in conjunction with a transparent phosphor-coated plate 90 and a conventional CRT mechanism. The volume of space between the baseplate 95, which holds the emission devices 85, and the phosphor-coated plate 90 is evacuated. When the emission device 85 is activated, electrons are accelerated from the cold-cathode field emission devices 85 towards the phosphor-coated plate 90, which serves as an anode and has a positive voltage relative to the emission devices 85. The phosphor on the phosphor-coated plate 90 is induced into cathodoluminescence by the bombarding electrons arriving at the phosphor surface via the same mechanism observed in conventional CRT technology and serves as the light source seen by a viewer. The electron beam flat panel display monitor 80 illuminates individual pixels, which are the bits which define the color and brightness of the picture or text elements. Therefore the power consumption of any one gun is proportional to the brightness of the pixel it is illuminating.
The operating system of a personal computer supplies certain functions that make up the interface between the application programs, the hard drives and the data on the volume (file system). Thus, the program (or computer system user) doesn't need to locate the individual data on the volume, or read one or more records into memory. Instead, the operating system returns all the requested data to the application (and therefore to the user) after a system call or command. Moreover, the operating system allows input and output of data through the parallel and series interfaces, and displays text and graphics on the display monitor. It manages main memory and allocates part of it to application programs. Therefore, the operating system controls and supervises the operation of the whole computer. An operating system which can manage several tasks in a computer system simultaneously, activating a task for a short time period and interrupting the task again later, is a multitasking operating system such as OS/2, UNIX or a Windows.RTM. based operating system. UNIX is a multitasking operating system for simultaneously serving several workstations. OS/2 is the multitasking successor to DOS (Disk Operating System) for IBM-compatible personal computers. Microsoft Windows.RTM. is a multitasking graphical user interface (GUI) environment that runs on Microsoft/MS-DOS-based computers.
The GUI is a type of display format that enables the computer system user to chose commands, start programs, and see lists of files and other options by pointing to pictorial representations (icons) and lists of menu items on the screen. Choices can generally be activated either with the keyboard or with a mouse. GUIs are used on the various multitasking operating systems. For example, Windows.RTM. based operating systems have an open programming interface which allows an invisible background task to track which GUI object currently has the user focus.
Most "windows" oriented operating systems reduce and increase the vibrancy of individual window borders in order to highlight which control or application area the computer system user is currently focused on. Typically, only application borders, captions and icons are utilized while ignoring large viewable display components such as application client windows and background wallpaper. This is done for information management purposes rather than power management.
An important design consideration for portable computers is power consumption. It is desirable to design portable computers to consume very little power during operation, thereby extending the duration of computer usage between battery charges. Visual display devices or monitors represent a significant portion of the power consumption for the entire portable computer. Therefore, there is a need to design a computer system which reduces the power consumption of visual display monitors.